The present invention generally pertains to telemetry systems and is particularly directed to an improved telemetry system for distributed equipment controls and equipment monitors.
As used herein the term telemetry system means a system for communicating control signals to equipment controls that are physically remote from the source of the control signals and/or a system for communicating monitored signals from equipment monitors that are physically remote from the receivers of the monitored signals. Many telemetry systems are used with remotely located computers which provide the control signals and receive the monitored signals.
Completing the communications links between the computer and the equipment controls and/or equipment monitors often requires complex masses of individual wires connecting each equipment control and/or equipment monitor to the computer. Such wiring is expensive to design, difficult to troubleshoot, and costly and time consuming to purchase and to install. A need to accomodate masses of wires on or within the structure of a equipment system often influences and restricts the design of the system.
Two prior art methods are available for the reduction of the complexity of interconnections in electrical equipment. These are frequency-division multiplexing and time-division multiplexing.
In frequency-division multiplexing, each signal to be communicated modulates a carrier at a unique frequency. The modulated carriers are then combined for transmission over a single wire pair or radio channel. At the receiving end, conventional frequency separation and demodulation techniques are used to separate the signals.
In time-division multiplexing, a single wire set is used to communicate a plurality of individual signals or signal sets by switching the wire set among the signal sources according to some prearranged time schedule or in accordance with prearranged, special commands. Complementary switching at the receiver directs the signals to their assigned destinations.